The first of Wikipedia's Five pillars, as we explained last week is the following, apparently mundane, statement: "Wikipedia is an encyclopedia".

This one should be pretty obvious, right? But then, what is an encyclopedia, exactly? You are probably imagining a wall of World Book editions at your school library. But you can be pretty sure those books didn't have an article about every Premier League footballer since 1992.

Generally speaking, if you picture a 21st-century version of those old hardback volumes, it's a good enough starting point. But Wikipedia is unique: with no limit on page count and an editorial community of thousands, Wikipedia's challenge is not deciding what to include but what not to include. (We'll spend more time on that a bit later in the series.)